Snap rings, also known as retaining rings
, are fasteners
that hold components or assemblies axially onto a shaft, or into a housing or bore. Typically installed in a groove, they are for one time use only. They are available in a wide variety of designs, materials, sizes, and with various improvements for different applications. Types of retaining rings include tapered section, constant section, spiral, and circular push-on. Tapered section snap rings decrease symmetrically toward the ends, to remain circular when contracted or expanded during use. They may be axially assembled, radially assembled, or self-locking. Axially assembled snap rings can be installed externally or internally, and are manufactured with lug holes for installation and removal. They can be inverted, beveled, or bowed, for specific applications. Radially assembled snap rings are only installed externally and feature no lug holes, instead being installed using applicators. Self-locking snap rings can be installed internally, or externally if there is no groove machined into the shaft. Constant section retaining rings feature a uniform section and material, causing elliptical deformation during contraction and expansion. Spiral snap rings make 360º contact with the groove, and can be installed internally or externally. They typically include a removal notch and can be manufactured in many different materials. Circular push-on rings are installed by pressing onto the end of the shaft, rather than threading a nut onto the shaft during the manufacturing process. Other snap ring designs include interlocking, circlip, and wire formed. Snap ring materials include copper, stainless steel, spring steel, and more. They commonly are treated with an outer coating to add protection and improve performance, such as zinc plating, phosphate coating, black oxide, cadmium plating, oil dip, nickel plating, or passivation.